Method and means for preventing tears in thermoplastic material



June 8, 1948. w.-s. CLOUD 2,442,757

METHOD AND MEANS FOR PREVENTING TEARS IN THERMOPLASTIC MATERIAL FiledApril 24, 1944 2 Sheets-Sheet 1 June 8, 1948. w. s. CLOUD 2,442,757

METHOD AND MEANS FOR PREVENTING TEARS IN THERMOPLASTIC MATERIAL FiledApril 24, 1944 2 Sheets-Shet 2- Patented June 8, 1948 IVIETHOD AND MEANSFOR PREVENTING TEARS IN THERMOPLASTIC MATERIAL William S. Cloud,Wilmette, Ill.

Application April 24, 1944, Serial No. 532,562

This invention relates to improvements in machines for stretching sheetsof thermoplastic material, and more particularly to a device formingmeans for preventing imperfections in thermoplastic material fromdeveloping into tears or runs when stretched.

It has been found that when thermoplastic material is heated andstretched, imperfections in the material may develop into small holes,which when force is applied to stretch the material, quickly developinto tears which will run the entire length of the sheet and destroy itsusefulness as a wrapping material for packaging purposes.

For example, this applicant has developed a machine for wrappingarticles in rubber hydrochloride, known to the trade as Pliofilm,disclosed in his co-pending application, Serial No. 436,666, filed March28, 1942 (abandoned June 17, 1946, after'filing of related applicationSerial No. 692,- 323), in which a rolled strip of Pliofilm is advancedover a heating drum, th'en grasped at its edges and stretchedtransversely and then longitudinally its length before entering thewrapping device. After the Pliofilm has been heated, the force appliedto impart the stretch sometimes causes any imperfections that may appearin the material to develop into small holes which quickly expand intolongitudinal tears, rapidly continuing to move backward along the stripto a region of equilibrium at which the stretching force continuouslysplits the oncoming sheet and destroys the purpose for which it is beingstretched.

The present application is directed solely to the feature of preventingtears in the web being stretched, and other features relating to thestretching of the web are reserved for application Serial No. 692,323.

It is an object of this invention to provide in such a machine means toprevent the development of such holes in the thermoplastic material fromexpanding as the material is being stretched to form tears that splitthe sheet.

With this and other objects in view, reference is made to theaccompanying sheets of drawings which illustrate a form of thisinvention with the understanding that detail changes may be made withoutdeparting from the scope thereof, and with the further understandingthat, while this invention is shown and described in one particular use,it is not restricted thereto and may be applied wherever thermoplasticmaterial is stretched for any purpose whatsoever.

In the drawings:

Figure 1 is a fragmentary, top plan view of a strip of Pliofilm as itenters a wrapping machine, illustrating diagrammatically the effect upona v 6 Claims. (01. 18-1) strip of Pliofilm of the appearance of a holein the material when being stretched.

Figure 2 is a view similar to Figure 1 illustrating diagrammatically themanner in which this invention prevents the spreading of a tear in thestrip.

Figure 3 is a fragmentary View in vertical, longitudinal section,illustrating the formation of a fold, crimp or rib in the heated stripofthermoplastic material.

Figure 4 is a fragmentary view in side elevation illustrating theoperation of the crimping device.

Figure 5 is a fragmentary view in section taken on the line 5-5 lookingin the direction of the arrows.

Figure 6 is an enlarged detail view illustrating the formation of afold, crimp or rib in the strip.

In recent years, there has been a demand for a material to be used forpackaging that will conform closely to the shape and size of thearticles with which it is used and at the same time afford a protectivecovering. A material whichanswers this demand is the rubberhydrochloride product sold by the Goodyear Tire and Rubber Company,Inc., of Akron, Ohio, under the trade name Pliofilm.

It is recognized that Pliofilm is a substantially moisture proof,transparent sheet material that becomes plastic when heated, and in thiscondition, it can be stretched easily to a considerable degree. Pliofilmhas been obtainable on the market in sheets of or gauge, %00000 or 91inch in thickness. It is also recognized, if heated sheets of Pliofilmare placed together, the sheets become attached or sealed to each Other.

This applicant has developed a' method and machine, as disclosed in hisprior co-pending application, Serial No. 436,666, filed March 28, 1942,now abandoned, whereby Pliofilm is stretched first laterally, ortransverse its length, and then longitudinally its length to a thicknessapproximately 20 gauge, 91 inch, prior to the wrapping of an articletherein. During the operation of this machine in stretching thethermoplastic Pliofilm, it has been found that imperceptibleimperfections, or weak spots in the stock become apparent, form smallholes in the heated film, and as it is stretched, develop into largerand larger holes, forming in effect, longitudinal runs in the directionof the length of the sheet, shown diagrammatically in Figure 1.Reference is made to the applicants said prior co-pending application asdisclosing the means for imparting the lateral stretch and thelongitudinal stretch to the heated thermoplastic film.

This applicant has discovered that, by forming a plurality of equallyspaced apart lateral or transverse folds, crimps or ribs in the heatedthermoplastic film just before the lateral stretch is initiated, thecreating and expanding of a hole in the sheet during the lateralstretching into a longitudinal run is confined or limited between thecrimps so that but a limited; portion: of the sheet is rendered uselessas a wrapper;

Figure 3 illustrates a strip of Pliofilm l unrolled from the roll 2passing over the heating device 3 between the idlers k andjf fi' anjditheir i o t "'aliyextendmgtsealed folds in the web and stretchover apackaging drum 6, assgeneransrdiscmsea in the applicant's said priorco-pending application.

has been accomplished and the longitudinal stretch is imparted, thethermoplastic material of the strip still being in a heated condition,the longitudinal stretching partially pulls out the folds 1 formed instrips so they become unobtrusive in the film as it is being employed towrap articles.

What I claim is:

1. The method of progressively stretching a web of plastic materialincluding the steps of formingaseries-of longitudinally spaced lateringthe web having said folds therein by moving its'sides'apart suflicientlyto substantially reduce abutment 8 is provided over which the heated.sncwn m th'e enlarged-detail view in 6 As shown in Figure 4, thetrunnions of-=-th' packaging:- drum 6- aremounteu in be'ar ingszupon'tlie'topi fl of. the-longitudinal side frames cf the machinewhich: alsesupportsr bearings 2" 'foii't'he oscillating transverse shaft Ill; Theshaft l e is provided with two radial extensions 13 to' which wemovable: abutment- -9 is: adjustably secured.

"rne -fixed abutment 1 8 *issupported upon two :muun'ted 'uponttheside'frame The w is 'o'scillated to' swing above the -upper surtace of 'thestrip o'f film: l by an arm: H5 carrid n one frame oathe machine; Atransverse-shaft 2a mounted in bearings on the side frame carries at onee'nd oppositely disposed cams II and-'- is rotated- 155 the same sourceof pow'er tfiat rotates the drum 6 causing the-- cams 2'! -tosuccessively wherever-a roller 22 'cai ried' en the tree arni 'of itlibell crank lever--t8 which canses-saict-lei 'er to osciilate agaihst thetension" oi -aspring--23 connected te=the opposite arm-theneofand ancholedi on th'e sicl'e' framee As the makmine in-tl' l'e applicants said-c'o -p'ending application advances strips of thermoplastic filmfromopposite ends of the machi-he-to'pass over-similar contactingpackaging drums; this invention -cei-itemplates providing-folds; crimpsor r'ib's' i'n each strip by a similar means; Having illu's tratedand-described the-folding or' crimping mechanismat; one end, itis notthough-t-n'eces sary tOdIIuSti-ate thesame mechanism at the opposite endas the shaft for corresponding to the shaft [0 may be oscillated'inunison there with by providing a secondarmlBa onshaf-t H1 andpivotallyconnecting it to a similar arm on' the end -of a corresponding shaft atthe other end o'f the machine by a pivoted-link liili, the arm L621andlink- I627 being shown in dotted lines in Figure 4. e

It hasbeen found that holes and runs iivl iich occur 'duringthe lateral"stretching: are usually adjacent tne longitudinal center of the strip sothat it is not-necessary to extend the-abutments 8 and 9 acrosstheentire widtnof theistripl -It lms alsc been found that after tlielateral stretch thethickness of the web.

2. Apparatus for progressively stretching a web of plastic materialincluding means for forming in the web a series of longitudinally spacedlaterally extending sealed folds'and means for'the'reaftermovingapart'thesides-o1 the wet; having saidyfoldstherein sufficientlyto substantially re ducerthe :thickness" of the we'bz."

3-. :The method of progressivelystretching a web of plastic materialincludingthe' steps of advancing the web in plasticand tacky condition,successively retarding: a small 1 portion of the" :web intermediate itssides long enough to cause: a piling lup of the advancing; web andthereby-produce :a laterally extending sealed fold; and stretching theweb having said foldsi thereln'by moving its sidesFapartsufficientIy tosubstantially reduce the thickness of the web.

4; Apparatus for progressively stretching 'a web of r plastic material"including means for advancingithe web in-plastic and tacky conditiom;means for engaging'a'smal-l; portion of the advancing web in'termediateof its 'sidesa-ndiholdingzit long enought'to retard the same" and cause.'a piling up of the advancing' web to produce a laterally extendingsealed fold-in; thmweb; anda-means' for thereafter" moving apart" thesides? of the web having said folds therein suflicientlytosubstantia'lly: reduce-the? thicknessioflthe' webl 5: Apparatus: forprogressively'stretclfing a; web at piastic material including meansfor.advancmg the web inaplastic andltackycondition',1means fort-engaging 1 asmall portion of i the advancing Web. intermediate ofits sl'clesand:holding it long enough to retard the-same and" camera) piling up; on theadvancing webto produce'a lateral-1y extendingsea'ledfold :instheweb,"and means for triereatteri moving apartwariou'sportions? oil theweb-"having said folds'thereln'sumciently tofsubstamtiallyrredizce thethickness of the web;

6'; Apparatus f'foriprogressively stretchin'gia'vweb of plastic materialincluding meansfor forniln'g in tlte web a; series of longit'udinallyspaced laterallyltextending sealed: folds and means io'r there"- after?moving Japarti portions: of the web having said: folds 'therle'ifzc'sumciently tor substantially reduce the thickness of :the w'e'b.

' S; CLOUD? REEERIENCES CITED The following references are of record inthe fil'e'eot th-is patent:

'wsrmnsmms PATENTS Number:

